Analysis of natural liquids at some distance from their natural situs is typically difficult because of changes in the sample environment as it is moved from the situs, questions as to the representative nature of the sample, and possible interactions with sampling and test equipment. Analysis of ground water, whether from aquifers, springs or surface streams, is especially sensitive to sampling and measuring conditions if accurate data are to be obtained.
Monitoring of water supplies is conducted periodically fo reasons of public health and regulatory compliance. Monitoring is likewise conducted in random situations where new wells are brought into service and where underground flows of water and their chemical characteristics are sought to be defined. Proper sampling of ground water seeks a close approximation to conditions where a well is producing water typical of the aquifer formation and not water modified chemically by conditions induced by the well itself. Geothermal liquids present different and complex problems generally due to high pressure, high temperature, and instability. Various techniques for the collection and analysis of ground water samples have been studied and guidelines have been developed by the Water Resources Division of the United States Geological Survey. However, improved sampling and analysis to provide a true picture of ground water supplies remains a matter of concern, particularly in a time when public awareness and concern for the nature and preservation of the environment is highly significant.
Analysis of ground water involves the determination of many parameters, some being very sensitive to analytical conditions. Such sensitive parameters include pH, oxidation-reduction (redox) potential (Eh), specific conductance, dissolved oxygen, temperature, and ferrous iron. Other mineral parameters are less sensitive to handling conditions. Other specialized parameters relate to colloidal and biological characteristics of the in situ ground water.
Despite extensive study given to this problem, there remains a need for methodology providing greater sensitivity and greater assurance of determination under precise conditions in ground water.